The invention also relates to an artificial lawn consisting at least of a backing to which one or more synthetic fibres according to the invention are attached.
Many sports, such as field hockey, tennis, American football, etc, etc, are currently played on artificial lawn as described in the introduction, comprising synthetic fibres as described in the introduction. Although sports people sustain fewer injuries when falling, making sliding tackles etc on natural grass sports fields, on account of the soft playing surface of natural grass, such sports fields sustain a great deal of damage precisely as a result of their intensive usage, in particular for the above sports, and as a result of the varying influence of the weather conditions.
Artificial lawns, on the other hand, require less maintenance and can be played on much more intensively than natural grass sports fields. Partly because of this, the synthetic fibres must have specific properties in order to be able to withstand the loads to which they are subjected as a result of being played on more intensively.
A drawback of the synthetic fibres that are currently known is that they tend to assume a flat orientation relative to the ground surface during use. This results in so-called “bare patches” in the artificial lawn and thus in an increased risk of injuries, etc.
This problem can be eliminated in part, for example by providing a granular infill material, such as sand or granules of a plastic material, between the synthetic fibres. The presence of these infill granules leads to a more upright orientation of the artificial glass fibres. Additionally, the infill granules not only provide a softer, shock-absorbing and thus less injury-prone surface. Furthermore, they lead to an improved style of play, so that the style of play on the artificial lawn will resemble the style of play on natural grass as much as possible.
The use of an infill in artificial lawns has a number of drawbacks. Not only is the installation of such an artificial lawn more labour-intensive than the installation of a natural lawn, but an artificial lawn provided with an infill requires subsequent maintenance as well. The initially uniform distribution of the granular infill can be disturbed by intensive usage. As a result, patches containing hardly any infill can develop in particular at places where the artificial lawn is played on very intensively, for example in the goal area, which has an adverse effect on the quality of play, but which above all leads to an increased risk of injury.
Another solution for the above-described problem is to increase the stiffness of the monofilament, which can be done by changing the chemical composition and/or the processing method. This is undesirable, however, because it will lead to a more abrasive artificial lawn with an increased risk of injuries.
Another solution for the problem as described above is to adapt the geometry of the synthetic fibre, for example as proposed in US 2001/033902 or in WO 2005/005730. Both patents disclose fibres comprising stiffness-enhancing agents. However, on account of the geometry of the fibre and the location of the stiffness-enhancing agents, a synthetic fibre is obtained which exhibits an increased risk of splitting and/or fracture due to material stresses that may develop in the fibre, for example caused by loads exerted thereon during play or temperature changes.
It is furthermore noted in this regard that US 2001/033902 discloses a composite filament fibre (also called multifilament) which, on account of its geometry and the orientation of the stiffness-enhancing agents, intentionally creates weak lines of fracture in the composite fibre. The fibre is intended to split so as to create multiple filament fibres.
Similar weak artificial fibres that are prone to splitting and/or fracture are disclosed in WO 2005/005730. Said publication, too, discloses a fibre comprising stiffness-enhancing agents, but said fibre, on account of its geometry, has undesirable points or lines of fracture at which undesirable material stresses can develop, for example under the influence of loads being exerted thereon during play (sliding tackles, etc.) or temperature changes.
WO 2005/005731 shows fibre geometries of synthetic fibres having an irregular cross-section. Due to the presence of thickened (or narrowed) parts (so-called “spines” or “buckles”), a concentration of material stresses will inevitably take place when loads are exerted thereon, which may lead to fracture or splitting.
U.S. Pat. No. 3,940,522 furthermore shows a fibre geometry in which the synthetic fibre is centrally provided with a thickened part, which thickened part is moreover located on one side of the fibre. Upon distortion, said fibre geometry will inevitably lead to undesirable material stresses, resulting in a buildup and concentration of material stresses at the location of the thickened part. Because of this, the fibre according to U.S. Pat. No. 3,040,522 is very prone to fracture and splitting and, unlike the fibre according to the invention, will not “buckle”.
WO 2006/085751 likewise shows all kinds of fibre geometries in which the synthetic fibre will not buckle upon being subjected to loads but rather fracture or split due to an undesirable concentration of material stresses.